1. Field of the Invention
The present invention relates to a ribbon drive apparatus for an impact printer.
In a typical impact printer, a type member is rotatable to select a desired type on the circumference of the type member, and a hammer is moved to strike paper against the type through a ribbon to print the character. It is desirable in devices such as printing electronic calculators to provide a ribbon with two colors of ink to provide emphasis of certain printout. The ribbon is therefore formed so that an upper portion of the ribbon is formed with ink of one color, for example black, and a lower portion of the ribbon is formed with ink of another color, for example red. It is also required to advance the ribbon after a character has been printed.
2. Description of the Prior Art
In prior art devices, complicated and expensive mechanisms comprising a clutch and cam, a plunger or pinion and rack and the like are employed to move a ribbon vertically to select the desired color for printing. Similar mechanisms which further include electric solenoids are used to advance the ribbon after each printing operation. These mechanisms generally have a tendency to move the ribbon by an amount which is just barely sufficient, so that the sharpness of the printed characters is sometimes marginal. The ribbon feed is performed after printing as a separate operation, thereby constituting low efficiency in printing.